[AMPS] HV Power Supply Project Example.
Tue, 8 May 2001 23:57:03 -0700
RE: HV Power Supply Project Example.
Hello from the Rotating Blackout zone...
I'm here to describe a High Voltage Power Supply
I've completed from mostly surplus parts. The
pictures should prove one can build a HV supply
for cheap money, serving in SSB Amplifier ps
service. Inventive part mounting hints are shown
that one might not normally think about. The power
supply case is a recycled computer tower.
This is a rather unconventional way of showing
this project via the amps list server. If your not
interested in the project or the pictures, just
delete this Email. Onward...
One can often find surplus transformers cheap, I've
seen a very common Collins Brand HV unit with dual
primaries, 2250 volt CT secondary @ ~500mA
removed from surplus transmitters. I've been able to
pick up a few through the years and figured it was
about time to use one. The secondary has a pretty
low resistance which lends it's use in doubler service
if desired. Surplus transformers are made like old
battle ships... big and heavy. This one's no exception.
Mounting of surplus transformers can sometimes
be a real hardware pain. The common bottom
stud bolted packages with same end connections
require extra layout considerations. I simply avoid
all the extra hardware by laying this style of xmfr
sideways, using a thick aluminum bracket to anchor
one side end down to the box bottom. Underneath is
a thin sheet of cut plywood cleaned and spray painted
gray to serve as a simple shock absorber. 1/4 inch
bolts are used and an ear bracket on the back wall
ensures the xmfr stays in position. A very solid
mount. I found the thin sheet of painted kiln dried
plywood idea was originally used in WWII aircraft
power supplies. The bottom bracket holds the wood
in place using 1/4 inch hardware.
Finding a great case or cabinet is as close as your
local Computer Surplus Parts Location. I've been
eye balling an old Compac 386 server case for some
time, when this project hit the burner... the case fit
the bill with minimal modification. I removed the
internals which included the AC supply and covered
the large supply hole with a suck out fan. A perfect
fit. Many available vent holes are located around
the box for air inlet.
The card slot holes were covered with original blank
slot covers and the keyboard/mouse hole areas
made a great place to place a plastic cover for HV
wire exit/entrance. The large AC cord is through a
chassis mounted strain relief.
The filter bank and diode boards were once part of a
very large and hefty Erbtec 6kv power supply. A trip to
the band saw separated the diode sections away
from the two separate filter banks. I obtained the
board for surplus weight prices off a popular on line
auction service. I'm under the impression one of
our trusty amps members had something to do
with the original Erbtec board design. It was a serious
3 phase power supply in its day.
Large square plastic blocks mount the boards in
place, you can see the cut diode board on the cab
bottom spacers. The GI Brand diodes are rated at
better than 3amp 6kv... wish I could find the source
for these "microwave oven spec units." The white
door knob bypass cap was scrounged surplus from
a laser ps. The poly plastic blocks were cut from
surplus material. Poly plastic is sold locally by
the pound at the surplus supply store.
The frame hole left by the original computer drive
bay makes an ideal front panel control location. A
square cut sheet of thick aluminum makes a nice
strong switch/metering/indicator mount.
A dual tied AC breaker switch, lamps meter and
metering points are placed on the front panel.
So it all went in the one box which fired up without
a hitch. Here the zero to 10KV meter shows almost
7KV no-load during initial testing. The indicator
lamps have not been wired yet.
The original ps supply couldn't have fit the bill
any better. Large non inductive resistors were used
in the original circuit, so I moved things around
and set up this 200 watt 15 ohm resistor for neg
lead metering. The ps ground connection to the
case is made with large ground braid. You can see
the fan in the back. Each of the cap bleeders are
100K 5 watt metal film resistors. Two on each
capacitor for equiv 50K ohm.
Put it all in place and get the last cover ready,
then snap a picture or two...
here's the circuit details:
Set up as a voltage doubler with a terminal
jack board to allow change over to a bridge
16, 450 volt hand matched capacitors in series
with 50K of bleeder resistance across each.
Each cap is surge rated to 525 Vdc.
Negative lead current metering through a 15
ohm 200 watt resistor. Front panel metered
zero to 10kv. Front panel AC on and cap bank
charged indication. Glitch resistors and
diodes along with bypass caps in place.
Front panel test point metering at chassis
ground, negative return and the hv divided
by 100. The red HV wire is rated to 40KV...
With covers on, has same profile as the original
Compac Server box it once was. Works very
well. Total cost, less than $100 Circuit
diagram available free upon request. Now
in service in a high speed pulser research
project, then it's off to amplifier service when
that project is completed.
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